Depression affects 1 in 4 individuals with type 2 diabetes, the principal manifestation of insulin resistance (IR), and is associated with hyperglycemia, diabetes complications, and mortality. Glycemic control improves significantly with depression treatment, and the gains are sustained throughout the subsequent depression- free interval. However, current depression treatment strategies fail to induce recovery in one-half of these patients and permit recurrence in one-third within a year. Several lines of evidence indicate that IR (depression-related or depression-independent) interferes with response to depression treatment and maintenance of the depression-free state. Therefore, we propose a two-phase (acute, 16 weeks;maintenance, 24 weeks), randomized, double-blind, placebo-controlled trial of treatment for major depressive disorder (MDD) in persons with IR, testing the following hypothesis: reduction in depression symptoms is greater (acute phase) and recurrence of depression is delayed (maintenance phase) in patients receiving insulin sensitizer augmentation of conventional antidepressant pharmacotherapy compared to patients treated with conventional pharmacotherapy alone. 200 subjects with MDD and IR [BMI >28.7 kg/m2 and homeostasis model of insulin resistance (HOMA-IR) >3.6] receive sertraline (SRT) and additional randomly assigned treatment with rosiglitazone (ROS) or placebo (PBO). For practical and ethical reasons, only patients with IR and without overt diabetes will be included. Those meeting criteria for MOD recovery will continue treatment for an additional 6 months while nonrecovered subjects will be referred for out-of- study depression management. Measures of depression, IR (from OGTT minimal model), glycemia, anthropometries, treatment adherence, physical activity and quality of life will be taken at baseline (pre- treatment) and the point of depression recovery/nonrecovery. In the recovered subset, additional measures will be taken at the time of MDD recurrence or 6 months after recovery in those remaining depression free. The primary endpoints are the reduction in depression symptom severity during the acute phase and elapsed time-to-recurrence (TTR) of MDD during the maintenance phase. Multiple regression (acute phase) and Cox proportional hazards models (maintenance phase) will be used to determine treatment effects as well as independent predictors of depression improvement and TTR. The principal hypotheses are that reduction in depression is greater and TTR is significantly longer in patients treated with SRT+ROS compared to those receiving SRT+PBO, and that reduction in IR independently predicts these favorable outcomes. If the hypotheses are supported, the study would have far-reaching scientific and public health implications: It will identify a novel treatment and a new treatment target for enhancing responsiveness to antidepressant therapy and lengthening the subsequent depression-free interval in patients with IR (With or without diabetes). The findings would represent a significant advance in depression treatment.